*{
    margin: 0;
    padding: 0;
    font-size: 0;
}

html, body{
    height: 100%;
}

#div1{
    width: 50%;
    height: calc(100% - 50%);
    background: #00c3ff;
    margin: 0 auto;
}

#div2{
    width: 50%;
    height: 50%;
    background: #ff0000;
    display: inline-block;
}

#div3{
    width: 50%;
    height: 50%;
    background: #00fd33;
    display: inline-block;

}